The present invention relates to a device for evacuating into the ambient air combustion products from a condensation boiler, in which at least one downstream section of the conduit for evacuating the combustion products is coaxial to the conduit for admission of the combustion air necessary for the burner and a fraction of the air collected in the admission conduit is returned towards the outside.
A condensation boiler aims at using to a maximum the energy of combustion of the gas, by cooling the smoke issuing from combustion as much as possible. In fact, the output of a boiler is known to be all the better as the outlet temperature of the combustion products is low and therefore as the quantity of heat carried away by this smoke is less. Taking into account the fact that the combustion products contain carbon dioxide gas and water, in a condensation boiler, the aim is to lower the temperature of the combustion products to below the dew point in order to allow a condensation of part of the water cotained in these combustion products and consequently release the recoverable heat.
In a condensation boiler, the surface of the exchanger between the smoke and the water to be heated is increased, or a second exchanger-recuperator between the smoke and the water to be heated is added to the main exchanger. The outlet temperature of the combustion products remains, by construction, slightly higher than the inlet temperature of the water to be heated (sanitary water or water coming from a radiator circuit). Consequently, the combustion products are often evacuated from the boiler at a temperature such that part of the total energy theoretically recoverable is lost.
Furthermore, the combustion products being cooled to saturation at the moment when they are rejected into the atmosphere, such rejection is accompanied, in a relatively cold atmosphere, by a wreath of vapour several metres long which is particularly unaesthetic when the point where the smoke emerges is located on the wall of a dwelling for example.